This invention relates to an outboard motor exhaust system and more particularly to an improved and simplified low-speed exhaust gas discharge for the outboard motor exhaust system.
As is well known, most outboard motors employ an exhaust system that has an underwater exhaust gas discharge through which the exhaust gases are discharged when operating at high speeds. Because of the compact nature of outboard motors, it is difficult to obtain the desired amount of exhaust gas silencing within the body of the outboard motor itself. By discharging the exhaust gases through the underwater exhaust gas discharge, the body of water in which the watercraft operates may be utilized as a silencing device, thus improving the silencing without making the outboard motor larger or more complicated.
However, when the watercraft is operating at a low speed, the underwater high-speed exhaust gas discharge is rather deeply submerged. This coupled with the lower exhaust gas pressures at low engine speed makes it difficult, if not impossible, to effectively discharge the exhaust gases to the atmosphere.
Therefore, most outboard motors employ, in addition to the high-speed underwater exhaust gas discharge, a low-speed above-the-water exhaust gas discharge. These above-the-water exhaust gas discharges are disposed so that their outlet ends are above the water level even when the watercraft is stationary in the body of water. Thus, the exhaust gases can be discharged through this above-the-water discharge when the engine is operating and the watercraft is either stationary or traveling at a low speed.
However, because of the inherent inability of the exhaust system within the driveshaft housing to totally silence the exhaust noises, the above-the-water exhaust gas discharge may produce objectionable noises. For that reason, it is the normal practice to include a series of baffles, expansion chambers, or other silencing devices formed within either the driveshaft housing, the spacer plate, the tray of the protective cowling, or a combination of these locations so as to silence the above-the-water exhaust gas discharge. However, these silencing devices are somewhat complicated and add to the difficulty and cost of forming the parts in which they are formed.
It is, therefore, a principal object of this invention to provide an improved and simplified exhaust gas outlet for an outboard motor.
It is a further object of this invention to provide an improved and simplified above-the-water, low-speed exhaust gas discharge for an outboard motor.
It is a further object of this invention to provide a simplified, but highly effective above-the-water exhaust gas discharge for an outboard motor.